In many data storage applications, there is a requirement for a disc drive having a high storage capacity within a small physical envelope. To satisfy this, Winchester type disc drives have come into common use. Such drives enclose one or more hard discs in a sealed enclosure designed in accordance with the above incorporated '690 patent application.
In such disc drives, where high storage capacity is contained within a limited space, it is important to provide a system in which the discs and read/write head assemblies remain precisely aligned, so that the data can be reliably accessed. With a need for increasing capacity, the circular tracks on the rotating disc on which data is stored are being moved closer and closer together. Thus it is essential that any sources of stress which might affect the precise alignment of the mechanical elements in th mechanical system must be eliminated.
It is a further problem occasioned by the close packing of adjacent data recording tracks, that any sources of contamination within the head disc assembly (HDA) must be eliminated. In the past, a common source of contamination has been the fact that screws are used to fasten the disc drive cover and base assembly together. When the screws were removed, or moved in their screw holes for another reason, they became a source of particulate matter within the HDA.
A further problem imposed by the use of screws in assembling the cover and base plate, was the fact that the tight fit created between these two pieces created stress in the base plate as the operating temperature of the base plate changed. Because of the position of disc drives within the computer, the base plate of a disc drive which supports both the spindle motor for rotating the disc and the actuator arm which carries the transducer for accessing the disc is subjected to significant thermal stress. In the absence of a way to relieve such stress, some relative movement of the actuator and spindle could occur, resulting in a misalignment of the transducer relative to the disc.
Finally, with the current move to 31/2" disc drives, and the many entrants in the field, cost has become a significant factor in the purchasing decision. The use of screws to bolt the top and bottom pieces of the HDA together represents a significant cost factor in the assembling process. It requires the use of a large number of parts, and is a function which is not easily automated. Therefore the problem to be addressed is to reliably clamp the pieces of the HDA together, while minimizing costs and avoiding the introduction of thermal or mechanical stresses which could result in misalignment of the mechanical elements of the system.